A traditional method of sealing the surface of a semiconductor component directly with a transparent resin involves using a photosensitive transparent resin, and exposing the resin to radiation through a photomask. The photosensitive resins commonly used in this method are acrylic-modified silicone resin compositions and silicone resin compositions that make use of photo-induced cationic polymerization. The materials of these types are transparent, but raise some problems when used for semiconductor component sealing. The acrylic-modified silicone resin compositions have poor heat resistance, so that they are likely to discolor on long-term use at elevated temperatures or under ultraviolet exposure. In the event that makes use of photo-induced cationic polymerization, the catalysts capable of generating cations upon light exposure contain many ionic impurities, most of which cause electrodes of aluminum or the like to be readily corroded.
On the other hand, thermosetting and room temperature curable silicone resin compositions are also used for the sealing of semiconductor components because they have a high purity and heat resistance as well as transparency and good adhesion. However, the materials of these types cannot be used when it is desired to seal only selected portions by direct imagewise processing of the material using radiation, typically ultraviolet radiation.
For the technology to which the present invention relates, reference is made to Epoxy Resin Handbook, pages 477–484, Nikkan Kogyo Newspaper Co., Ltd.